Forward head posture (FHP) angle and plantar pressure resulting from oscillatory stimulation training of the shoulder joint: A randomized controlled trial

Abstract

BACKGROUND:

OBJECTIVE:

This study aimed to investigate the difference in average distribution of plantar pressure resulting from changes in the forward head position (FHP) angle caused by controlling muscle activity in the neck and shoulders through Bodyblade.

METHODS:

The subjects were divided into an experimental group (Bodyblade, $n=$ 15) and a control group (general physiotherapy, $n=$ 15). Eighteen sessions of exercise were implemented. Craniovertebral angle (CVA) and cranial rotation angle (CRA) were measured to evaluate the change of FHP. The Gaitview AFA-50 (Alfoots Co, Korea) was used to measure the plantar pressure distribution.

RESULTS:

The experimental group showed a larger increase in CVA than the control group ( $p<$ 0.05). Only the experimental group showed a significant decrease in CRA ( $p<$ 0.05).

Both the anterior pressure and posterior pressure showed a significant improvement only in the experimental group ( $p<$ 0.05). The experimental group showed a larger increase in anterior/posterior ratio than the control group ( $p<$ 0.05).

CONCLUSIONS:

Bodyblade improves the angle of FHP, thus positively affecting the average ratio of plantar pressure.

Keywords

Head posture plantar pressure Bodyblade

1. Introduction

The human body has a multi-joint system comprising a kinetic chain wherein a series of connected joints interact with each other by muscle activity and are controlled by a central nervous system [1]. Prolonged improper posture causing problems in one part of human body can set off a chain reaction of poor alignment and imbalance.

The current trend of extended use of computers and smartphones causes users to maintain abnormal posture alignment of the head and neck for long periods, resulting in forward head posture (FHP). FHP entails flexion of the head forward and upward, increasing the load on the muscles and joints of the neck and shoulders [2]. This results in spine malalignment and muscle imbalance. The continued, abnormal contraction of shoulder muscles may cause the upper thoracic vertebrae to become hunched in compensation [2, 3], which, in turn, changes the position of the shoulder blades [4]. This causes an imbalance between the shoulder blades and the humerus, as it affects the muscles that control arm function, which consequently induces functional impairment of the shoulder joint [4, 5]. Moreover, continued positioning in a hunched posture not only increases flexion of the head, but also increases the line of force of body weight in upper body and external moment arm between lumbar vertebrae. This increases pressure on the intervertebral discs [6, 7].

Lumbar hyperlordosis occurs when kyphosis increases beyond the normal range in the thoracic vertebrae on the sagittal plane [8]. The S-shaped lordosis in the sagittal plane plays a major role in maintaining balance by properly distributing body weight. However, conditions such as scoliosis and posture deformities such as FHP shift the body’s center of gravity, inducing dynamic change in posture and affecting the torso and joints. Balance is also altered as a physical response to such conditions. Such imbalance of weight support by the lower limbs diminishes balancing ability [9].

Foot plantar pressure measurement is used mainly to diagnose balancing and walking problems. Abnormal plantar pressure can cause scoliosis, in particular excessive pressure on the heel of the foot, which also causes FHP and increases neck and shoulder pain [10, 11].

The movement of a body segment forms a kinetic chain from the proximal end to the distal end and the movement of a distal segment requires control of the proximal segment [12]. Given this, an exercise program aimed at relieving FHP must include shoulder and arm exercise. Improving balance control necessitates increasing spinal stability during functional posture and movement. Normal motor sense is required to correct one’s posture; one must be able to receive sensory input from the sensory receptors distributed in the skin, muscles, and joints [13].

Oscillatory stimulation provides strong sensory stimulation, which can activate muscle spindles, strengthening proprioceptive sense and, therefore, helping to strengthen the muscles involved in posture stability. Oscillatory stimulation may also be applied to patients with muscle control imbalance, as it can reduce abnormal muscle tension [14].

Bodyblade (Mad Dogg Athletics, USA) is an oscillatory device which may be used as an effective rehabilitation aid to reinforce dynamic and static shoulder stability [15]. Bodyblade is a flexible bar which the user shakes, creating oscillatory stimulation proactively. As resistance is provided to the body while oscillatory stimulation is generated from the distal end to the proximal end of a body segment, proprioceptive sense is stimulated. The simultaneous contraction and eccentric contraction of muscles act to increase muscle stability [16, 17]. Training with the Bodyblade is reported to be effective in enhancing stability of the shoulder joint and core stabilization of the torso as well as training the muscles that stabilize the spine [18]. This implies that Bodyblade training can be an effective method for improving shoulder blade and spine stability. However, no study has yet examined how shoulder joint stability obtained from Bodyblade training improves FHP or how the change of FHP angle affects the weight distribution of plantar pressure.

The present study investigates the difference in average distribution of plantar pressure resulting from changes in the FHP angle caused by controlling muscle activity in the neck and shoulders through Bodyblade training in patients with FHP. The purpose of this study is to provide fundamental data to inform recommendations for easily accessed therapy programs for patients with FHP.

2. Material and methods

2.1 Subjects

Patients hospitalized or receiving outpatient treatment for neck pain at Hospital S, located in G City, Korea, were selected as the subjects of this study. The research period was from December 2015 to March 2016. Following the ethical standards set by the Declaration of Helsinki, the purpose and procedure of this study were sufficiently explained to all the subjects before the experiment. The subjects voluntarily agreed to participate in the experiment. The participating subjects were then randomly divided into an experimental group, which performed Bodyblade exercise, and a control group, which performed general physiotherapy, each group comprising 15 members.

Subjects with a craniovertebral angle (CVA) below 52 ${}^{\circ}$ and a cranial rotation angle (CRA) over 143 ${}^{\circ}$ were selected through a primary posture evaluation before the experiment. Patients with inborn spinal deformity, those with surgical histories due to spine and shoulder illness, those incapable of maintaining a natural head posture when measuring FHP, those with neurological disorders, and those who performed regular neck and shoulder exercise were excluded from the sample. All subjects were right arm dominant.

2.2 Exercise program

The experimental group trained with the Bodyblade Classic (Mad Dogg Athletics, AL, USA), an exercise tool comprising a flexible pole measuring 122 cm in length, 4.3 cm in width, and 0.68 kg in weight. The user holds the blade-shaped tool by a handle at its center and shakes it, generating oscillation at a constant frequency and speed. As a baseline posture, the subjects set their feet at shoulder width and slightly flexed the knees while standing upright. The intervention comprised two types of exercise, or exercise tasks, designed to improve forward head posture (FHP). The intensity, duration, and frequency of the exercise were determined by referring a previous study [18].

(I) The first exercise task was an oscillation exercise in the sagittal plane in an overhead posture: the subjects held the center of the blade with both hands overhead, with the blade perpendicular to the floor and the shoulder joints flexed at approximately 180 ${}^{\circ}$ . (II) The second exercise task was also an oscillation exercise in the sagittal plane with the blade parallel to the floor, this time with the shoulder joints flexed at 90 ${}^{\circ}$ . The exercises were assigned in a random order. A total of 18 sessions of exercise were implemented during the study period, with 3 sessions a week for 6 weeks. Each session was composed of 4 sets, and each set comprised 3 minutes of exercise followed by 5 minutes of rest.

Physiotherapy was provided to all subjects in both the experimental and control groups, consisting of 20 minutes of a hot pack, 15 minutes of transcutaneous electrical nerve stimulation (TENS), and 5 minutes of ultrasound therapy applied to back of the neck and areas of the shoulders where patients indicated pain.

2.3 Measurement of craniovertebral angle and cranial rotation angle

CVA and CRA were measured to evaluate the change of FHP. For the measurements, the subjects stood with their arms loose at their sides in a natural, balanced posture with a natural head posture while standing comfortably [19]. Image diagnosis equipment (PROTEUS XR/A, GE Healthcare Co, USA) was used to take lateral images of the subjects. CVA and CRA were measured by drawing a line between the 7th cervical vertebra and the tragus, and another line between the tragus and the lateral canthus, and measuring the angle between the two lines. The average measurement from two images was used. Smaller CVA angles and larger CRA angles indicate more serious FHPs [20].

2.4 Measurement of plantar pressure

The Gaitview AFA-50 (Alfoots Co, Korea), a resistance-type, pressure sensor measurement device, was used to measure the plantar pressure distribution. The Gaitview has 2,304 pressure sensors distributed on a measuring board with the following dimensions: 410 $\times$ 410 $\times$ 3 mm. The sensors measure alignment and weight loading of subjects in both a standing position (static) and walking, in a relative ratio. The data collected from Gaitview pro 1.0 software were analyzed.

Before measuring the static plantar pressure, the barefoot subjects marched in place for two or three steps. The subjects then stepped onto the measuring board and maintained a standing position for 15 seconds with their arms at rest at their sides for the measurement. In the distribution of support of static plantar pressure, the sum of the support distribution ratio of anterior pressure and posterior pressure and the sum of the support distribution ratio of left and right plantar pressure becomes 100%, each of which is divided into two with 50% as a criterion. The subjects’ plantar pressure was measured twice. The average value of the distribution of weight of the anterior and posterior plantar pressure was computed. A distribution ratio was then obtained by calculating the average value of the difference between the anterior and the posterior plantar pressure.

Table 1
General characteristics for exercise and control groups

	Exercise group	Control group	p
Gender (M/F)	3/12	8/7
Age (years)	20.60 $\pm$ 4.04	23.00 $\pm$ 5.33	0.18
Height (cm)	165.45 $\pm$ 8.70	166.69 $\pm$ 5.86	0.65
Weight (kg)	63.40 $\pm$ 13.43	59.71 $\pm$ 8.62	0.38

Values are expressed as the mean $\pm$ standard deviation.

2.5 Statistical analysis

SPSS for Windows (version 22.0) was used to analyze the data in this study. A paired t-test was used to examine the difference between measurements taken before and after the intervention. An independent t-test was used to examine the difference in measurements between the subject groups. Cohen’s d was used to measure the effect size between the two groups. Statistical significance was defined at $\alpha=$ 0.05.

3. Results

Table 1 describes the general characteristics of the subjects.

Comparing measurements taken before and after the intervention, CVA significantly increased in both the control group and the experimental group ( $p<$ 0.05). The experimental group showed a larger increase in CVA than the control group ( $p<$ 0.05). After the intervention, only the experimental group showed a significant decrease in CRA ( $p<$ 0.05) (Table 2).

Table 2
Comparisons of CVA and CRA between groups and between pre- and post-test (unit: angle, ${}^{\circ}$ )

Group	Pre		Post		p	Cohen’s d
CVA
Control	48.86	$\pm$ 2.13	50.38	$\pm$ 3.77 ${}^{*}$	0.03	0.61
Exercise	48.39	$\pm$ 2.76	55.49	$\pm$ 3.48 ${}^{*{\dagger}}$	0.00	1.64
p	0.59		0.01
CRA
Control	148.05	$\pm$ 4.28	147.70	$\pm$ 4.63	0.62	$-$ 0.13
Exercise	149.68	$\pm$ 5.39	142.94	$\pm$ 4.26 ${}^{*{\dagger}}$	0.01	$-$ 1.10
p	0.36		0.01

Values are expressed as the mean $\pm$ standard deviation. ${}^{*}p<$ 0.05, within-group comparison. ${}^{\dagger}p<$ 0.05, between-group comparison. CRA, Cranial Rotation Angle. CVA, Craniovertebral Angle.

Table 3

Comparisons of foot pressure and A/P ratio between groups and between pre- and post-test (unit: percent, %)

Group	Pre	Post		P	Cohen’s d
Anterior pressure
Control	42.13 $\pm$ 4.39	44.55	$\pm$ 3.73	0.11	0.46
Exercise	40.16 $\pm$ 4.31	48.19	$\pm$ 4.56 ${}^{*{\dagger}}$	0.00	1.36
p	0.23	0.03
Posterior pressure
Control	58.20 $\pm$ 6.07	56.16	$\pm$ 3.05	0.28	$-$ 0.30
Exercise	59.84 $\pm$ 3.54	51.81	$\pm$ 5.89 ${}^{*{\dagger}}$	0.00	$-$ 1.19
p	0.37	0.02
Left pressure
Control	49.94 $\pm$ 3.31	50.22	$\pm$ 3.90	0.96	0.01
Exercise	49.53 $\pm$ 2.64	50.23	$\pm$ 3.72	0.47	0.19
p	0.71	0.99
Right pressure
Control	50.06 $\pm$ 3.31	49.77	$\pm$ 3.90	0.96	$-$ 0.01
Exercise	50.47 $\pm$ 2.64	49.76	$\pm$ 3.72	0.47	$-$ 0.19
p	0.71	0.99
A/P ratio
Control	0.73 $\pm$ 0.06	0.79	$\pm$ 0.08 ${}^{*}$	0.45	0.59
Exercise	0.68 $\pm$ 0.09	0.94	$\pm$ 0.15 ${}^{*{\dagger}}$	0.00	1.55
p	0.74	0.04
L/R ratio
Control	1.01 $\pm$ 0.13	1.02	$\pm$ 0.16	0.98	0.01
Exercise	0.99 $\pm$ 0.10	1.01	$\pm$ 0.15	0.38	0.23
p	0.62	0.99

Values are expressed as the mean $\pm$ standard deviation. ${}^{*}p<$ 0.05, within-group comparison. ${}^{\dagger}p<$ 0.05, between-group comparison. A/P ratio, anterior/posterior pressure ratio. L/R ratio, left/right pressure ratio.

Comparing foot pressure measurements before and after the intervention, both the anterior pressure and posterior pressure showed a significant improvement only in the experimental group ( $p<$ 0.05). Both the control group and the experimental group showed a significant increase in anterior/posterior (A/P) ratio after the intervention ( $p<$ 0.05). The experimental group showed a larger increase in A/P ratio than the control group ( $p<$ 0.05) (Table 3).

4. Discussion

The FHP patients in the experimental group performed Bodyblade exercises in the sagittal plane for 6 weeks to correct muscle activity in the neck and shoulders and to stabilize the shoulders affected by bad posture. A comparison analysis was conducted on the average distribution of plantar pressure in relation to the change in the angle of the neck.

Spondylolisthesis due to bad posture is accompanied by abnormal location of the shoulder blades and lack of dynamic stability, and causes functional impairment due to the way that the human body compensates for bad posture [7]. Thigpen et al. [5] reported that FHP posture change alters the shoulder blade movement and muscle activity involved in raising the hands overhead.

This study examined the use of shoulder exercise on the sagittal plane using Bodyblade in an overhead posture as an intervention scheme to alleviate FHP. Harman et al. used CVA and CRA to measure change in FHP. In general, a decrease in CVA below 50 ${}^{\circ}$ is accompanied by pain and the normal range of CRV is larger than 145 ${}^{\circ}$ [20]. In the present study, CVA significantly increased (55.49 $\pm$ 3.48 ${}^{\circ}$ ) and CRA significantly decreased (142.94 $\pm$ 4.26 ${}^{\circ}$ ) in the subjects following the intervention.

This study found the enhanced mobilization of the alpha-motorneurons in shoulder and neck muscles during the oscillatory stimulation induced by the Bodyblade exercises to increase CVA and decrease CRA. Because shoulder blade is stabilized thanks to the controlled muscle activity of shoulder muscle by nerve root control, global muscle strengthening, and proprioceptive feedback, it can be inferred that this activity plays a role in improving neck posture [14].

To maintain proper posture in a static, standing position, weight must be properly balanced and proper muscle tension is required. Proper balance requires that information regarding the body’s location and movement be delivered to the central nervous system via normal sensory input from the somatosensory and cochleovestibular systems [22]. Posterior cranial rotation takes place to correct view as normal lordosis is lost in cases of FHP, causing the extensor and flexor muscles in the neck to stretch. As a result, the body’s center of gravity shifts forward, affecting balance [23].

Balance refers to the ability to spread one’s weight equally and thus control posture and keep from swaying or falling [24]. FHP causes a plantar pressure imbalance and diminishes balancing ability by shifting the body’s center of gravity forward. In this study, the subjects’ anterior and posterior static plantar pressure was (ratio $=$ 0.68 $\pm$ 0.09) before the intervention. As the center of gravity is shifted forward in cases of FHP, the upper backbone hunches to compensate for this. As a result, weight is shifted posteriorly to restore proper balance [25].

In the present study, the anterior and posterior static plantar pressure was (ratio $=$ 0.94 $\pm$ 0.15) following the Bodyblade exercise. These results can be attributed to the increased CVA and decreased CRA following the intervention, which consequently shifted the center of gravity anteriorly. This implies that size of vertical loading of plantar pressure according to the shift of the center is related to the change of the center of gravity [6].

In the study by Oliver et al. [26], healthy subjects conducted total body shoulder exercise using bodyblade for 6 weeks. This six-week intervention resulted that the peripheral muscles of the lumbopelvic-hip complex (LPHC), the core region connecting the upper extremity to the lower extremity, are activated to improve the stability of the pelvis, thereby positively affecting limb movements. These results support those of this study that bodyblade training can improve the stability of the trunk and the lower extremity movement control ability, thereby positively affecting the foot pressure.

Gravant et al. [11] reported that abnormal plantar pressure can induce scoliosis and that large differences between anterior and posterior plantar pressure can cause problems in the musculoskeletal system as the differences affect the ankle joints.

This study has limitations in that it did not take into account any deformities of the foot, such as flatfoot. Nevertheless, the study finds that Bodyblade exercise results in a change in the angle of FHP, thus affecting the average ratio of plantar pressure in a stable standing position. The study concludes that a rehabilitation program which activates the entire kinetic chain of distal and proximal parts of the body, such as with the Bodyblade, can be effective to treat neck and shoulder disorders.

Footnotes

Conflict of interest

None to report.

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